The invention relates to a method for operating an internal combustion engine.
In internal combustion engines, the fuel quantity that is being supplied to the internal combustion engine must be adjusted. When the environmental conditions change or the filled-in fuel type has changed the supplied fuel quantity must be adjusted accordingly. The correlation between the engine speed that is generated and the supplied fuel quantity is defined by an operating curve for otherwise unchanged operating conditions; such an operating curve has an ascending branch, a maximum, and a descending branch. The ascending branch characterizes the lean range of the mixture and the descending branch indicates the rich range of the mixture.
For adjusting the fuel quantity that is to be supplied it is known to determine on which branch of the operating curve the operating point of the internal combustion engine is located and, based thereon, to adjust the desired operating point. This is realized usually in that the supplied fuel quantity is reduced and the engine speed response of the engine is evaluated. When the operating point is located on the ascending branch of the operating curve, the engine speed will drop. When the operating point is located on the descending branch of the operating curve, the engine speed will increase when the mixture becomes lean. In particular at idle of the internal combustion engine, a further leaning of the mixture when the mixture is already very lean can cause the internal combustion engine to stall.